An acoustic shield is mounted to a fixture holding an aircraft turbofan assembly by means of self-lubricating DryLin T Profile Rail guides.

By Ellen Rathburn, Technical Copywriter, igus, Inc., East Providence, RIAircraft noise is a major concern of students in the University of California at Irvine's Aeroacoustic Laboratory. Students within UCI's Aeroacoustic Laboratory recently worked with DryLin® T Profile Rail rail guides donated by plastics innovator igus®, Inc. as part of The Geared Turbofan Project, to study the noise attenuation effects of a hybrid wing-body in relation to the placement of an aircraft's turbofan. As part of the laboratory, the students study the acoustics of aerospace technologies, including moving parts such as fans and nozzles.

This particular experiment was funded by a major aerospace contractor, The Boeing Company (www.boeing.com). The experiment involved the placement of a noise shield under an aircraft turbofan to measure the attenuation of noise in the downward direction. Traditional aircraft have a main fuselage, two large wings, and engines mounted below the wings. Most of an aircraft's lift comes from the two wings and the engines mounted below them, which are traditionally unshielded in terms of acoustic noise. The widely used hybrid-wing-body (HWB) design, also known as a blended wing body, has a fuselage with smooth mechanical transition into the wings. One advantage of this design is that the airfoil-shaped body assumes most of the lift so that an aircraft can operate effectively with smaller wings. The design also creates less "deadweight" surface area, which prevents the aircraft from losing lift or dragging. Another advantage, currently under study at UCI's (UC Irvine) Aeroacoustic Laboratory, is the attenuation of downward noise. When engines installed above the fuselage employ a noise-shield, it results in less acoustic noise for those on the ground beneath the aircraft.

Acoustic experiments were performed in an anechoic chamber capable of detecting and recording acoustic noise to 120 kHz.

To study the effectiveness of the noise-shield design, a small-scale model of the geared turbofan engine was built and tested in an anechoic chamber. The nacelle and fans were made using stereolithography three-dimensional (3D) printing, and the fan was powered by a brushless DC motor, typically used in extreme-performance radio-controlled (RC) planes. To simulate the presence of the fuselage below the engines, a simple noise-shield was made in the shape of the HWB platform provided by Boeing Co. The shield itself is made from 1/8-in.-thick aluminum sheets and is nearly six feet long from wingtip to wingtip in order to match the scaling of the nacelle and fan.

Lubrication-Free Solution
The noise-shield was mounted on the model HWB platform using DryLin T profile rail guides and manual clamp carriages. The linear guide system makes it possible to study the noise attenuation effects of the turbofan placement relative to the backend of the shield. The manual clamp carriages are bolted onto the metal fixture holding the turbofan assembly, so that the noise-shield can be easily slid forward and backward in relation to the nacelle. Unlike recirculating linear ball guides, DryLin T profile guide rails use self-lubricating glide pads, which require no greasing or external lubrication. The DryLin T guide rails are designed to provide a cost-effective, maintenance-free solution for applications such as this.

These miniature rail guide systems are based on self-lubricating DryLin T materials from igus, Inc.

According to Tae Kim, a member of the UCI Aeroacoustic Laboratory team, "The DryLin T rails and carriages withstand the torque of the heavy shield." Kim added that "If a simple bar of metal had been used, the shield would have needed to be detached from the bar and then reattached at a different location with screws and nuts. The DryLin rail and carriages allows for easy movement of the shield, which eliminates the risk of screws falling. [It also] allows the shield to move at very small increments, which expands the scope of the study. The pre-drilled holes on the rails made it easy to mount and the mach inability of the rails allowed for easy adjustments in length."

In conjunction with the company's Young Engineers Support (Y.E.S) Program, igus donated the DryLin T profile rail guides at no cost to the UCI students. The Y.E.S. Program aims to foster the mechanical design ideas of students with a passion for engineering, while at the same time educating them on the merits and benefits of plastic components. The DryLin linear bearings and linear guides are designed to run without additional lubrication or maintenance, minimizing the downtown associated with ball-bearing systems requiring additional lubrication. The materials used in the DryLin T profile rail guides are resistant to dirt, dust and chemicals and other harsh environments.